1. Field of the Invention
This invention relates to a casing for a reflection measurement device such as a device for measuring the distance to a reflective object by using a light beam or a radar device using a laser beam.
2. Description of the Related Art
A typical on-vehicle reflection measurement device emits a forward laser beam from the subject vehicle, and controls the forward laser beam to scan a prescribed area outside the subject vehicle. In the case where an object exists in the prescribed area, the forward laser beam encounters the object before being at least partially reflected thereby. Generally, a portion of the reflected laser beam returns to the measurement device as an echo laser beam. The measurement device converts the echo laser beam into an electric echo signal. The measurement device processes the electric echo signal into data for object recognition or detection purposes.
Such an on-vehicle reflection measurement device can be used in an apparatus for alerting a driver when an obstacle (for example, a preceding vehicle) to the subject vehicle is detected. Also, the measurement device can be used in an apparatus for controlling the speed of the subject vehicle to maintain the distance from a preceding vehicle in a safe range.
The on-vehicle reflection measurement device is provided with a casing for housing members and parts of the device. The casing has an outlet window via which the forward laser beam is propagated. The casing also has an inlet window via which a return laser beam (an echo laser beam) enters the device. Plate-like protective covers transparent to laser beams extend over the inlet and outlet windows, respectively. The protective covers are supported by inner surfaces of the walls of the casing. The protective covers prevent pebbles and raindrops from entering the casing.
The upwardly-facing surface of the walls of the casing which defines the lower side of the outlet window is exposed to the atmosphere. Rainwater tends to be collected on this wall surface. When the forward laser beam meets the collected rainwater and passes therethrough, it is scattered and partially absorbed thereby. As a result, the power of the forward laser beam reaching an object, and also the power of a return laser beam coming from the object are reduced. The power reduction causes a decrease in the detectable distance to an object.
Japanese patent application publication number 11-38122 discloses a casing for a reflection measurement device. The casing in Japanese application 11-38122 has drain grooves to enable rainwater to escape from the lower side of an outlet window. During the manufacture of the casing, a special processing step is required to make the drain grooves.
Japanese utility model application publication number 4-54746 discloses an on-vehicle laser radar device. The laser radar device in Japanese application 4-54746 includes a cylindrical hood provided on a front of a laser radar head. The hood covers a laser emitting section and a laser receiving section. During the travel of the subject vehicle, wind coming from the front thereof acts as a dynamic pressure in the hood. Under rainy conditions, the dynamic pressure directs raindrops toward the sides of the hood, thereby preventing them from meeting the front surface of the laser radar head.
Japanese utility model application publication number 5-14961 discloses an inter-vehicle distance measurement device using a laser beam. The measurement device in Japanese application 5-14961 has a front surface covered with a lens. A wiper is provided to clean a surface of the lens. Cleaning liquid can be injected from a nozzle toward the lens surface. A dirt sensor acts to detect dirt on the lens surface. The injection of cleaning liquid from the nozzle and the drive of the wiper are controlled in response to the output signal of the dirt sensor.
It is an object of this invention to provide a casing for a reflection measurement device which can be manufactured without a special processing step, and which can prevent rainwater from collecting in the lower edge of an outlet window.
A first aspect of this invention provides a casing for a reflection measurement device emitting a scanning beam and receiving an echo beam caused by reflection of the scanning beam at an object, and detecting a distance to the object in response to the received echo beam. The casing comprises a window through which a beam is transmitted; and a protective member being transparent to the beam and internally covering the window. The window provides a predetermined range through which the beam passes, and an interval between a lower edge of the beam pass range and a lower edge of the window is greater than an interval between opposing edges of the beam pass range and the window which differ from the lower edges thereof.
A second aspect of this invention provides a casing for a reflection measurement device emitting a scanning beam and receiving an echo beam caused by reflection of the scanning beam at an object, and detecting a distance to the object in response to the received echo beam. The casing comprises a window through which a beam is transmitted, and a protective member that is transparent to the beam and that internally covers the window. The window provides a predetermined range through which the beam passes, and an area of a zone between a lower edge of the beam pass range and a lower edge of the window is greater than an area of a zone between opposing edges of the beam pass range and the window which differ from the lower edges thereof.
A third aspect of this invention is based on the first aspect thereof, and provides a casing including a casing member defining the window and a resilient member provided between the casing member and the protective member and non-projecting into the window.
A fourth aspect of this invention is based on the first aspect thereof, and provides a casing wherein the lower edge of the window inclines at a predetermined angle relative to the lower edge of the beam pass range.
A fifth aspect of this invention is based on the first aspect thereof, and provides a casing wherein the window has a pentagonal shape with a downwardly-projecting lower side.
A sixth aspect of this invention is based on the first aspect thereof, and provides a casing wherein the lower edge of the window tapers as viewed in a direction perpendicular to a plane of the window.